diff --git a/example/example_int/example_int.go b/example/example_int/example_int.go
index 5ebed3b..efd294f 100644
--- a/example/example_int/example_int.go
+++ b/example/example_int/example_int.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"fmt"
+
 	"github.com/HuKeping/rbtree"
 )
 
@@ -28,10 +29,10 @@ func main() {
 		m++
 	}
 
-	rbt.Ascend(rbt.Min(), Print)
+	rbt.Ascend(rbt.Min(), print)
 }
 
-func Print(item rbtree.Item) bool {
+func print(item rbtree.Item) bool {
 	i, ok := item.(rbtree.Int)
 	if !ok {
 		return false
diff --git a/example/example_string/example_string.go b/example/example_string/example_string.go
index f55f422..dee5341 100644
--- a/example/example_string/example_string.go
+++ b/example/example_string/example_string.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"fmt"
+
 	"github.com/HuKeping/rbtree"
 )
 
@@ -15,10 +16,10 @@ func main() {
 	rbt.Insert(rbtree.String("Hello"))
 	rbt.Insert(rbtree.String("World"))
 
-	rbt.Ascend(rbt.Min(), Print)
+	rbt.Ascend(rbt.Min(), print)
 }
 
-func Print(item rbtree.Item) bool {
+func print(item rbtree.Item) bool {
 	i, ok := item.(rbtree.String)
 	if !ok {
 		return false
diff --git a/example/example_struct/example_struct.go b/example/example_struct/example_struct.go
index 62b2fff..6ce89c1 100644
--- a/example/example_struct/example_struct.go
+++ b/example/example_struct/example_struct.go
@@ -6,16 +6,18 @@ package main
 
 import (
 	"fmt"
-	"github.com/HuKeping/rbtree"
 	"time"
+
+	"github.com/HuKeping/rbtree"
 )
 
+// Var is the node of a struct
 type Var struct {
 	Expiry time.Time `json:"expiry,omitempty"`
 	ID     string    `json:"id,omitempty"`
 }
 
-// We will order the node by `Time`
+// Less will order the node by `Time`
 func (x Var) Less(than rbtree.Item) bool {
 	return x.Expiry.Before(than.(Var).Expiry)
 }
@@ -56,10 +58,10 @@ func main() {
 	}
 
 	// var4 and var5 were expected
-	rbt.Ascend(rbt.Get(tmp), Print)
+	rbt.Ascend(rbt.Get(tmp), print)
 }
 
-func Print(item rbtree.Item) bool {
+func print(item rbtree.Item) bool {
 	i, ok := item.(Var)
 	if !ok {
 		return false
diff --git a/iterator.go b/iterator.go
index 35aeade..a4d77e6 100644
--- a/iterator.go
+++ b/iterator.go
@@ -4,6 +4,18 @@
 
 package rbtree
 
+// Iterator is the function of iteration entity which would be
+// used by those functions like `Ascend`, `Dscend`, etc.
+//
+// A typical Iterator with Print :
+// func loop_with_print(item rbtree.Item) bool {
+//         i, ok := item.(XXX)
+//         if !ok {
+//                 return false
+//         }
+//         fmt.Printf("%+v\n", i)
+//         return true
+// }
 type Iterator func(i Item) bool
 
 // Ascend will call iterator once for each element greater or equal than pivot
diff --git a/rbtree.go b/rbtree.go
index 66dff9f..bc77a38 100644
--- a/rbtree.go
+++ b/rbtree.go
@@ -15,6 +15,8 @@ package rbtree
 //  5) Every simple path from root to leaves contains the same number
 //     of black nodes.
 //
+
+// Node of the rbtree has a pointer of the node of parent, left, right, also has own color and Item which client uses
 type Node struct {
 	Left   *Node
 	Right  *Node
@@ -26,10 +28,13 @@ type Node struct {
 }
 
 const (
-	RED   = 0
+	// RED represents the color of the node is red
+	RED = 0
+	// BLACK represents the color of the node is black
 	BLACK = 1
 )
 
+// Item has a method to compare items which is less
 type Item interface {
 	Less(than Item) bool
 }
@@ -48,6 +53,7 @@ func less(x, y Item) bool {
 // New returns an initialized Red-Black tree
 func New() *Rbtree { return new(Rbtree).Init() }
 
+// Init returns the initial of rbtree
 func (t *Rbtree) Init() *Rbtree {
 	node := &Node{nil, nil, nil, BLACK, nil}
 	return &Rbtree{
diff --git a/stats.go b/stats.go
index c8333d4..64f9d66 100644
--- a/stats.go
+++ b/stats.go
@@ -8,9 +8,10 @@ package rbtree
 // by the user. Anyone who wants to look for some API about
 // the rbtree, this is the right place.
 
-// Number of nodes in the tree.
+// Len returns number of nodes in the tree.
 func (t *Rbtree) Len() uint { return t.count }
 
+// Insert func inserts a item as a new RED node
 func (t *Rbtree) Insert(item Item) {
 	if item == nil {
 		return
@@ -32,6 +33,7 @@ func (t *Rbtree) InsertOrGet(item Item) Item {
 	return t.insert(&Node{t.NIL, t.NIL, t.NIL, RED, item}).Item
 }
 
+//Delete delete the item in the tree
 func (t *Rbtree) Delete(item Item) Item {
 	if item == nil {
 		return nil
@@ -41,6 +43,7 @@ func (t *Rbtree) Delete(item Item) Item {
 	return t.delete(&Node{t.NIL, t.NIL, t.NIL, RED, item}).Item
 }
 
+//Get search for the specified items which is carried by a Node
 func (t *Rbtree) Get(item Item) Item {
 	if item == nil {
 		return nil
@@ -55,12 +58,14 @@ func (t *Rbtree) Get(item Item) Item {
 	return ret.Item
 }
 
+// Search does only search the node which includes it node
 //TODO: This is for debug, delete it in the future
 func (t *Rbtree) Search(item Item) *Node {
 
 	return t.search(&Node{t.NIL, t.NIL, t.NIL, RED, item})
 }
 
+// Min return the item minimum one
 func (t *Rbtree) Min() Item {
 	x := t.min(t.root)
 
@@ -71,6 +76,7 @@ func (t *Rbtree) Min() Item {
 	return x.Item
 }
 
+// Max return the item maxmum one
 func (t *Rbtree) Max() Item {
 	x := t.max(t.root)
 
diff --git a/util.go b/util.go
index 737f4af..dcb2e36 100644
--- a/util.go
+++ b/util.go
@@ -4,14 +4,18 @@
 
 package rbtree
 
+// Int is type of int
 type Int int
 
+// Less returns whether x(Int) is smaller than specified item
 func (x Int) Less(than Item) bool {
 	return x < than.(Int)
 }
 
+// String is type of string
 type String string
 
+// Less returns whether x(String) is smaller than specified item
 func (x String) Less(than Item) bool {
 	return x < than.(String)
 }